The overall objectives of this project are to study the mechanisms underlying the changes in visual sensitivity during light adaptation and dark adaptation. Specifically, we plan to examine in psychophysical experiments whether and under what conditions the rod and cone systems contribute independently or interactively to control visual sensitivity in the near peripheral retina in humans. We are particularly interested in those rapid sensitivity changes that occur during the first few hundred milliseconds near the onset or the offset of a background field, i.e., early light adaptation and early dark adaptation.